Calendar - Perpetual
The perpetual calendar is even more complicated than the annual calendar. It displays the same information as the annual calendar, but does not even require adjustment in February. It knows the year in relation to the next leap year (i.e. it keeps track of years in four-year cycles), so is able to automatically account for leap years. It rarely needs to be adjusted - because of the oddity of leap years, a perpetual calendar will need to be adjusted next in 2100.